EXPRESS: Positional Impact on Ocular Lens and Thyroid Radiation Doses During Feline Cranial CT: A TLD Study of 70 Cases.

OBJECTIVES: The increasing use of computed tomography (CT) in feline medicine necessitates the optimization of radiation protocols to adhere to ALARA principles. This prospective study aimed to evaluate the impact of patient positioning dorsoventral (DV) versus ventrodorsal (VD) on radiation doses absorbed by the ocular lenses and the thyroid gland during feline cranial CT. METHODS: Seventy cats were divided into two equal groups (DV, n = 35; VD, n = 35). Radiation doses were measured using thermoluminescent dosimeters (TLD-100) placed at the anatomical projections of the target organs. RESULTS: While no statistically significant difference was observed in ocular lens doses between the groups (p > 0.05), VD positioning resulted in a 24.4% reduction in the mean radiation dose absorbed by the thyroid gland compared to the DV position (1.33 ± 0.17 mGy vs. 1.76 ± 0.35 mGy, respectively; p = 4.97 × 10⁻⁹). This reduction is attributed to the "natural shielding" effect provided by the dorsal axial skeleton and epaxial muscles in the VD position. CONCLUSIONS AND RELEVANCE: VD positioning offers a significant dosimetric advantage for protecting the thyroid gland without requiring additional equipment or compromising diagnostic quality. Adopting the VD position as a routine standard in feline cranial CT is recommended to minimize radiation exposure to the thyroid gland.